Combined NAH and Beamforming Using the Same Microphone Array
Jørgen Hald · Sound&Vibration · 2004
This article deals with the problem of how to design a microphone array that performs well for measurements using both Nearfield Acoustical Holography (NAH) and Beamforming (BF), as well as how to perform NAH processing on irregular array measurements. NAH typically provides calibrated sound intensity maps, while BF provides unscaled maps. The article also describes a method to perform sound intensity scaling of the BF maps in such a way that area-integration provides a good estimate of the sub-area sound power. Results from a set of loudspeaker measurements are presented. Figure 1 shows a rough comparison of the resolutions on the source plane, R BF and R NAH , that can be obtained with BF and NAH, respectively. The resolution is here defined as the smallest distance between two incoherent monopoles of equal strength on the source plane that allows them to be separated in a source map produced with the method in consideration. For BF the near-axial resolution is roughly